During that research expedition, we learned that possession by ghost pokémon only happens if the subject is weak-willed or if the subject invites a ghost-type to possess them. Of course, all three of us have naturally strong wills due to the rigors of our studies, and among us, Bill is the only one who has undergone additional meditative training specifically designed to build resistance to psychic and spiritual influences, thanks to his prolonged exposure to a kadabra.
Unfortunately, all the training and rigorous study habits in the world mean absolutely nothing when you lack your Scottish ancestors’ legendary alcohol tolerance but possess, in its stead, an insatiable curiosity as well as the belief that the best way to interact with a pokémon is directly, usually by way of inviting it to do—and I quote—“whatever it would do naturally.”
—LH
On the positive side, we gained a lot of valuable data from that. —Bill
Bill, we were forced to chain you to the floor. —LH
The Pokédex According to Bill 